1© 2011 The MathWorks, Inc.

Designing Control Systemsfor Wind Turbines

Steve Miller

Technical Marketing, Physical Modeling

MathWorks

Root Locus Bode Plot

Real Axis Frequency

Park

Startup

Brake

Generating

http://www.mathworks.com/physical-modeling/

Grid

Pitch

Yaw

RotorSpeed

Blades

Tower

Geartrain GeneratorHub

Lift

Wind

2

Key Points

The time to develop a controlsystem can be shortened byusing control design tools

Optimizing systems with respect to design requirements leads to optimal design choices

Finding errors in supervisorycontrollers requires a modelthat can be easily built, understood, and tested

Control+-

A x + B u

Root Locus Bode Plot

Real Axis Frequency

3

Agenda

Wind turbine control system overview Compensator design for pitch control system

– Using linear control theory

– Applying optimization algorithms to nonlinear model Supervisory control using state machines

4

Grid

Wind Turbine Control Systems

Yaw

GeneratorSpeed

Tower

Geartrain Generator

Pitch

RotorSpeed

Blades

Hub

Lift, DragWind

Nacelle

Blade pitch control system– Adjust pitch angle to regulate

rotational speed Supervisory control system

– Analyze operating conditions to determine state of turbine to enable/disable operation

5

Controlling Rotor SpeedUsing the Pitch Angle

Problem: Control the pitch angle so that the generator shaft spins at nominal speed

Solution: Use Simulink to determine the pitch angle by controlling the angle of attack

Model:

DesiredRotor Speed

Desired Angleof Attack

Control

ActualRotor Speed

InflowAngle

Pitch AngleCommand

+-

Pitch

RotorSpeed

Lift

6

Overview of Pitch System

ControlActuator

Pitch AngleCommand

Measured Pitch Angle

DetermineState

Event Based Control System changes mode based on events

Compensator Design Actuation is based on deviation from a commanded value (PID, etc.)

7

Agenda

Wind turbine control system overview Compensator design for pitch control system

– Using linear control theory

– Applying optimization algorithms to nonlinear model Supervisory control using state machines

8

Control+-

Possibilities for Compensator Design

Linear Control Theory– Linearize system using Simulink

Control Design– Perform linear control design with

Control System Toolbox– Retest controller in nonlinear system

A x + B u

Root Locus Bode Plot

Real Axis Frequency

Control+-

Specify System Response– Specify response

characteristics

– Automatic tuning using Simulink Design Optimization

9

Control Design on Linearized Plants

Problem: Design and test a controller for a nonlinear system using linearmethods to meet system specifications

Solution: Use Simulink Control Designand Control System Toolbox to design, tune, and test the controller

Model:

A x + B u

Root Locus Bode Plot

Real Axis Frequency

Comm

and

Error

Force

Pitch

Angle

Control+-

10

Control Design on Linearized Plants

Steps to Design Controller1. Identify control loops of interest

2. Identify operating point

3. Linearize model about this point

4. Perform control design

5. Test controller in nonlinear system

A x + B u = 0

Actuat

or

Force

Pitch

Angle

Comm

and

Control+-

Root Locus Bode Plot

Real Axis Frequency

11

Control Design on Linearized Plants

Advantages of Simulink Control Design and Control System Toolbox

1. Enable easy application of linear control theory Operating points from specification or simulation Graphical design with interactive plots

2. Rapid evaluation of designs with interactive analysis plots

3. Automatic tuning of parameters through various methods (PID, IMC, LQG) saves time

4. Optimize performance based on time, frequency, or root locus constraints

12

Agenda

Wind turbine control system overview Compensator design for pitch control system

– Using linear control theory

– Applying optimization algorithms to nonlinear model Supervisory control using state machines

13

Compensator Design on Nonlinear Plants

Problem: Design and tune thecontroller in this system tomeet system requirements

Solution: Use Simulink Design Optimization to design, tune, and test the controller

Model:

Kp Ki

7000 4

Kp Ki

92845 317

+-(Kps+Ki)

s

(Kps+Ki)s

14

Compensator Design on Nonlinear Plants

Steps to Optimize Response

1. Identify parameters to be tuned

and their ranges

2. Specify desired response

3. Perform response optimization

(Kps+Ki)s

15

Compensator Design on Nonlinear Plants

Advantages of Simulink Design Optimization

1. Graphical interface makes it easy to map specification to tests.

2. Automatic tuning of parameters saves time.

3. Simulating plant and controller in one tool allows engineers to understand and optimize performance of the entire system.

16

Agenda

Wind turbine control system overview Compensator design for pitch control system

– Using linear control theory

– Applying optimization algorithms to nonlinear model Supervisory control using state machines

17

Model the SupervisoryControl of the Wind Turbine

Problem: Create a supervisory controller that sets the state of the brake, generator, and pitch angle based on turbine conditions

Model:

Solution: Use Stateflow to model the event-based controller

wind > cut in speed &&wind < cut out speed

turbine > min speed

wind spd < min spd || wind spd > max spd

|| turbine spd < min spd|| turbine spd > max spd

Turbine spd< park spd

park brake = 0pitch brake = 0generator = 0

Startuppark brake = 0pitch brake = 0generator = 1

Generating

park brake = 0pitch brake = 1generator = 0

Brakepark brake = 1pitch brake = 0generator = 0

Park

18

Key Points

The time to develop a controlsystem can be shortened byusing control design tools

Optimizing systems with respect to design requirements leads to optimal design choices

Finding errors in supervisorycontrollers requires a modelthat can be easily built, understood, and tested

Control+-

A x + B u

Root Locus Bode Plot

Real Axis Frequency